This patch implements a simple version of the SMP Pairing Features
exchange procedure (Vol. 3 Part H, Section 2.3.5.1).

For now, everything that would cause a Pairing Method different of
Just Works to be chosen is rejected.
Signed-off-by: NVinicius Costa Gomes <vinicius.gomes@openbossa.org>
Signed-off-by: NGustavo F. Padovan <padovan@profusion.mobi>